In recent years a number of systems have been developed to provide two-way data communications between computers and computer-support equipment installed throughout a building or a group of buildings within a local area. These systems are generally known as Local Area Networks (LANs). One popular implementation of a LAN is the "bus" topology, in which a communications medium or "bus" is routed along a path running near each user station, and a short "stub" branches off the main bus to connect to the station.
With current technology, there are two major shortcomings to LANs implemented in such a bus topology: 1) as the total length of the bus becomes longer and the number of users increases, the efficiency of the network decreases because only one user can be allowed to transmit on to the bus at any time; and 2) due to the asynchronous manner in which the bus access is allocated to each user, the network cannot provide voice telephone services. The invention is intended to improve upon this situation.
Another common network to which the invention is addressed is the CAble TeleVision (CATV) network. The CATV network topology can be described as a "tree", where central system equipment connects to the "trunk" of the tree, which then extends out towards the subscriber sites, splitting off into "branches" along the way, which in turn split into more branches as more users are connected. Amplifiers are installed along the way to compensate for signal losses. In the typical cable TV application, signals originate in the head end and travel in one direction only--"downstream" on the cable toward the subscribers.
CATV networks service a large and increasing number of homes and businesses in the United States. Computers are installed at many of these locations and the need to provide data communications services to these computers is increasing. In addition, voice telephone services are typically required at these locations. Some CATV operators have experimented with two-way communications over the cable for "pay-per-view" television programming and "home shopping" services, but these have not proved to be economically viable. Due to the limitations of current technology, CATV network operators are generally unable to offer full duplex (two-way) voice and data communications services to their subscribers because a feasible, cost effective technology for implementation of dial-up two-way digital services over the CATV cable has not been available.
It is noted that current technology does exist for providing dedicated point-to-point two-way digital communications over coaxial cable systems. This is done by "splitting" the cable bandwidth into an upstream and a downstream frequency band, one allocated to signal transmission in each direction, and transmitting suitably modulated RF carriers in each direction over the cable. A common implementation of this type of system uses the digital telephone technology known as "T1" to provide digital voice/data services to clients requiring 20 or more voice-equivalent channels between two fixed points on the cable. The "T1 channel bank" is a synchronous time division multiplex technique which combines 24 digital channels into a single bit stream at 1.544 MB/s.
However, this technology is not cost-effective for providing services to large numbers of independent subscribers distributed randomly down the cable who individually require only 1 or 2 voice or data channels on a dial-up basis, because there is no way to allocate the 24 channels of one upstream T1 channel bank to different subscribers located at different places along the cable. The reason is that current technology does not accomplish the synchronizing of all transmissions in the upstream direction from a plurality of subscribers with the downstream T1 format, as does the invention.